health Where Did I Go Wrong - Yellow Leafs

[pa1966stang]

Things were chugging along normally with my seedlings this year until I did the first transplant. Since then, everything has started to yellow over the past 2 weeks and now things are looking very sickly. Below is a recap of the specifics:
 
1. seeds started 6 weeks ago. 
2. fertilizing with .5-.5-0 seed starting fertilizer
3. seeds started with sterilize starting mix
4. grow light on 18 hours a day
 
Replanting Info:
1. replanted into 4" pots 2 weeks ago
2. leaves starting to go yellow and drop
3. one flat of un-transplanted seeds are still green and doing well (see pics)
4. tomatoes and peppers are affected. Oddly enough, watermelon is doing fine. 
5. repotted with a bag a potted plant soil from HD
 
 
Any ideas what wrong? At first I was thinking over watering, but I personally have been letting them dry out very much between waterings. I'd like to blame the soil. Either way, these guys may or may not limp through the rest of the summer, but luckily there is a great greenhouse and I was able to replace most of the non-obscure seedlings this morning. 
 
Some pictures are attached. 
 
TW

 

[Chilidude]

They might be just running out of nutrition, buy something that is complete food for plants and use that.

 

[CAPCOM]

Too wet. I beleive you are over watering and the media is too compacted and the roots drowning.
In addition, dont start fertz so soon. They dont need anything till a couple sets of true leaves have grown out.
 

 

[Chilidude]

Too wet. I beleive you are over watering and the media is too compacted and the roots drowning.
In addition, dont start fertz so soon. They dont need anything till a couple sets of true leaves have grown out.
 

 
I believe you are correct after reading the text a little more carefully.
 

 

[CAPCOM]

Its not to late, there is still green in them.
 Get a better media, some MYKOS and transplant using as little of the existing media as you can. even washing most of being careful of the roots will work. dont forget the MYKOS at this point (IT IS A VERY IMPORTANT COMPONENT).
 

 

[moruga welder]

I also so to wet , are they inside still ?

 

[pa1966stang]

Yes, they were still inside up until yesterday. I made the transition to putting them outside under shade cloth yesterday afternoon. I am taking a split the difference approach. Since most of my garden beds were ready, I put 1/2 of them into the ground figuring the amended soil in the beds would solve the junk soil issue. The other 1/2 I am going to transplant one more time with better soil. 
 
A little further inspection shows that all might not be lost. There are leaves already starting to re-grow on the nodes of some of the lower branches. I didn't have my phone to snap a picture, but hopefully these guys make a strong comeback and don't end up just limping through the entire summer. 
 
Thanks for the insight and help, I had a feeling it was too much water. Interestingly enough I didn't change my watering schedule when I put them into the larger pots. Maybe that soil just stayed more moist. 
 
TW